Our long-term objective is to develop safe and effective methods for comprehensive gene-based therapies for mucopolysaccharidoses, which are characterized by lysosomal glycosaminoglycan (GAG) deposition, resulting from inherited deficiency of enzymes needed for stepwise degradation of GAGs. Because GAG deposits affect multiple systems, including the liver, spleen, bones, brain and eyes, gene therapy for these disorders present a special challenge. In this project, we will target mucopolysaccharidosis-VTI (MPS-VII, beta-glucuronidase deficiency, Sly syndrome), since a well-characterized murine model is available. In preliminary studies, we have shown that transfer of the beta-glucuronidase (GUSB) gene using recombinant SV40-based vectors has the potential to ameliorate the GAG deposits in the brain as well as in the liver and spleen. The first specific aim is to optimize SV40- based vectors for safe and efficient systemic gene transfer. Novel viral gene-deleted vectors will be generated to accommodate promoters for efficient long-term transgene expression in various tissues. Insulators will be introduced to protect neighboring genes in the host genome from being accidentally activated by enhancers within the vector. In Specific Aim 2, we will determine optimal routes of administration, efficacy of gene transfer, tissue and serum GUSB levels and reduction of GAG-containing lysosomal vesicles. In addition to evaluating phenotypic correction of the liver and spleen, special emphasis will be placed on gene transfer to various types of brain cells in different regions of the brain after intravenous, intracerebro-ventricular or intracerebral injection of the vectors. We will also determine the potential of injecting these vectors into newborn or fetal mice on the ability to correct GUSB deficiency early in development, thereby preventing early brain damage, which is common in MPS VII. Since SV-40-based vectors are non-toxic, non-immunogenic and capable of integrating into the host genome, successful completion of this project should provide a safe and effective method for comprehensive molecular therapy of all forms of lysosomal storage disorders that are associated with visceral, skeletal and central nervous system injury.